High intensity bursts of light, commonly referred to as strobe lighting, are useful in a variety of applications. Flashes of high intensity light may be delivered at regular intervals to create special effects for photography or to "freeze" the motion of an object where the lamp discharge frequency is synchronized with the movement. Further, the intensity of the output light from a flash tube is visible in daylight ambient conditions and may be used in both daytime and nighttime lighting to serve as a warning signal or a position marker.
By way of example, tall structures such as broadcast antennas are provided with strobe lights to warn aircraft. Likewise, aircraft use strobe lighting to identify their position to other aircraft in their vicinity. Rapidly firing strobe lights are used on emergency vehicles to direct attention to the moving vehicle and to warn traffic ahead of the vehicle.
Conventional circuits for use with a flash tube are generally analog-type devices. The high voltage necessary to produce an intense light flash is commonly generated from a blocking oscillator circuit using a bipolar power transistor. The output waveform from the blocking oscillator circuit is applied across the primary windings of a transformer. The oscillating current in the primary windings may then be varied rapidly enough to induce a high voltage in the secondary windings of the transformer according to well established principles. The high voltage generated across the secondary windings, in turn, produces a current which is stored in high voltage capacitors. The voltage across the storage capacitors will increase as current is cyclically delivered to these capacitors.
A timing circuit must also be provided in order to deliver the energy stored in the high voltage capacitors to the flash tube. Conventionally, independent circuitry is provided for generating the timing signals. An integrated circuit may be configured as an oscillator with reference timing determined by a connected resistor-capacitor (RC) circuit.
The output from the timing circuit is applied to the control lead of an SCR to connect the circuit containing the storage capacitors to the flash tube. The stored energy is used by the flash tube to generate the high intensity light output from the system.
In conventional strobe light circuitry, high voltage transients may be induced across various circuit elements because of the voltages induced in transformer windings from rapidly changing current conditions. Such high voltage transients may severely damage circuit components.
Further, conventional circuitry may permit solid state devices to waste large amounts of the input energy in the form of heat. While heat sinks can be provided to assist in dissipating the heat, the resulting high temperatures may severely shorten the life span of the device. Also, heat generation is an inefficient use of input power, which may be stored energy from a finite source.
In addition, conventional flash tubes may often be used with conventional circuits for only a short time. As flash tubes age they frequently require additional recovery time before the tube may be discharged again. The recovery may be impeded, or even stopped, by the application of electrical signals to the tube during the recovery which would otherwise be insufficient to discharge the tube.
Conventional strobe tube circuits also generally fail to automatically accommodate changes in ambient light conditions in any way. The same light intensity may be delivered during full daylight as during nighttime. In one variation, a switch is provided to enable an operator to manually select a higher intensity output for daylight strobe visibility.
These and other disadvantages of the prior art are overcome by the present invention and improved methods and circuitry are provided for generating power and control pulses for use in flash tube activation generating high intensity strobe light pulses.